A PLAN to salvage the cargo of crude oil from the sunken tanker Prestige is being considered by the European Commission. As 91av went to press, Smit International, a Rotterdam-based salvage company, was set to tell the Commission that it will cost between €20 and €30 million to recover the 60,000 tonnes of oil that remain on the wreck.
The Prestige, which split in two and sank on 19 November, is lying 3.5 kilometres down on the floor of the Atlantic, some 200 kilometres off the north-west coast of Spain. Oil has never been recovered from a depth of more than 2 kilometres. “We think it’s technically possible,” says Lars Walder of Smit. “But it will be extremely difficult.”
Smit proposes lowering a remotely operated drill and pump onto the Prestige. It will bore a 15-centimetre hole near the top of the hold and connect up a pipe to the surface. Rapeseed oil will then be pumped down from the surface and mixed with oil from the hold to thin it. The mixture will then be pumped up a second pipe to barges on the surface. One problem the salvagers will have to cope with is the rough water in the Atlantic. “The wave height is about 4 to 5 metres,” says Walder. “So we will need large ships.”
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The decision on whether or not to salvage the oil is ultimately a political one for the Spanish government, which is being helped in the clean-up effort by a number of other European countries. In economic terms, the oil isn’t worth recovering. “The salvage cost exceeds the value of the oil,” says Walder. “But it’s cheaper than the cost of cleaning up if the oil escapes.”
Oil is currently leaking from the tanker’s bow section at the rate of 50 litres an hour, says Guy Herrouin of IFREMER, the French Research Institute for Exploitation of the Sea. IFREMER’s submarine, the Nautile, has been surveying the wreck over the past week on behalf of the Spanish government. Some 9000 tonnes of oil have already washed up on the Spanish coast, damaging the fishing industry and devastating wildlife. And the oil keeps coming ashore. “There’s as much again to come,” says Kevin Colcomb of Britain’s Maritime & Coastguard Agency (MCA), which is helping Spain to fight the slick.
About 23 kilometres of floating booms have been deployed to keep the slick away from rivers and low-lying marshes. But much of the coast is too exposed and seas too choppy for booms to work. “A 5-metre swell is far too rough for booms,” says Colcomb.
Experts had expected the remaining oil on the Prestige to solidify in the cold waters of the seafloor. The MCA has calculated that the temperature of the oil would be below its “pour point” – the minimum temperature at which the oil will flow. “We were a bit surprised to see the leak,” says Colcomb.
He points out that that the leak is relatively small, however. “There are a lot of natural subsurface releases of this size,” he says. Herrouin adds that the hole is only 10 to 15 centimetres across, and it might be possible to stem the flow by laying a metal plate over the breach.
